It has been known that color development of an exposed silver halide color photographic material causes reaction between an oxidized aromatic primary amine development agent and a coupler to form a dye such as indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine or the like, thus a color image being formed. In this process, color reproduction is usually attained according to subtractive color photography using silver halide emulsions selectively responsive to blue, green and red light, together with agents capable of forming yellow, magenta and cyan color, are respectively in complementary relation with blue, green and red.
Yellow color images are formed by using, for example, acylacetanilide type or benzoylmethane type couplers, magenta color images are formed by using, primarily, pyrazolone type, pyrazolobenzimidazolone type, cyanoacetophenone type or indazolone type couplers, and cyan color images are formed by using, primarily, phenolic couplers such as phenols and naphthols.
Color couplers must meet various requirements; for example, they must possess good spectral characteristics and, upon color development, provide dye images having high stability to light, temperature, and humidity over a long period of time.
In multi-layered color light-sensitive materials, respective couplers must be immobilized in separate layers for the purpose of reducing color mixing and improving color reproduction. Many techniques are known for rendering couplers diffusion-resistant or non-diffusible.
One technique is to introduce a long-chain aliphatic group into a coupler molecule for preventing coupler diffusion. Couplers in accordance with this technique must be rendered alkali-soluble to add to a gelatin aqueous solution due to their immiscibility with water, or must be dissolved in a high-boiling organic solvent to emulsify and disperse in a gelatin aqueous solution.
Such color couplers can cause precipitation of crystals in an emulsion or, when a high-boiling organic solvent is used, require a large quantity of gelatin for softening the emulsion layer, resulting in an increase in thickness of the emulsion layer, which is contrary to the general desire of thinning emulsion layers.
Another technique of rendering couplers diffusion-resistant is to utilize a polymer coupler latex obtained by introducing a polymerizable group into coupler molecule and polymerizing the resulting coupler.
Examples of processes of adding a polymer coupler to a hydrophilic colloid composition in a latex form that have conventionally been known include a process of directly adding to a gelatino-silver halide emulsion a latex prepared by emulsion polymerization, and a process of dispersing an olephilic polymer coupler, obtained by polymerization of monomer coupler, in an aqueous gelatin solution as a latex. Examples of the former emulsion polymerization process include U.S. Pat. No. 3,370,952 which describes an emulsion polymerization process in aqueous gelatin, and U.S. Pat. No. 4,080,211 which describes an emulsion polymerization process in water. Examples of the latter process of dispersing an oleophilic polymer coupler as a latex are described in U.S. Pat. No. 3,451,820.
The process of adding a polymer coupler in latex form to a hydrophilic colloid composition has many merits over other processes.
First, since the hydrophobic material is in latex form, the material does not adversely affect the strength of membrane formed, and, since the latex can contain monomer coupler in a high concentration, the coupler can be easily incorporated in emulsion in a high concentration without a detrimental increase in viscosity.
In addition, it has a further merit that, due to the prevention of any transfer of the coupler, no color mixing and less precipitation of coupler in emulsion membrane take place.
Of such polymer couplers, magenta polymer couplers added in a latex form to gelatino-silver halide emulsion are exemplified by those described, for example, in U.S. Pat. Nos. 3,451,820, 3,926,436 and 4,080,211, British Pat. No. 1,247,688, West German Pat. No. 2,725,591, etc. In general, however, magenta color images formed by these conventionally known magenta polymer coupler latexes have the defect that their absorption wave form is broader than the color images formed by the analogous non-polymerized type magenta couplers, leading to deterioration of color reproducibility. Further, 5-pyrazolone type nuclei-containing magenta polymer coupler latexes that have so far been mainly studied show an desirable absorption of yellow component around 430 nm, which causes color stain.
U.S. Pat. No. 3,725,067 describes use of 1H-[5,1-c]-1,2,4-triazoles (not polymers) as magenta couplers. However, these magenta couplers have defects in that they have a small solubility in high-boiling organic solvents, and they show only a comparatively low coupling activity in ordinary developing solutions. Thus, in the case of adding necessary amounts of them to silver halide emulsions as an oil dispersion, the emulsion layers must be thickened, tending to lead to a deterioration of sharpness.